When it floods in California, the culprit is usually what’s known as an atmospheric river—a narrow ribbon of ultra-moist air moving in from over the Pacific Ocean. Atmospheric rivers are also essential sources of moisture for western reservoirs and mountain snowpack, but in 1861, a series of particularly intense and prolonged ones led to the worst disaster in state history: a flood that swamped the state. The megaflood turned the Central Valley into an inland sea and washed away an estimated one in eight homes. What would happen if the same weather pattern hit the state again? Los Angeles Times reporter Louis Sahagun and University of California, Los Angeles climate scientist Daniel Swain join Ira to discuss the storms, its potential impact on local infrastructure, and why disastrous flooding events like the one in 1861 are not only becoming more likely as the planet warms, but may have already been a more frequent occurrence than previously thought. Plus: As a grad student in astrophysics at Cambridge University, Priya Natarajan devised a theory that might explain a mysterious relationship between black holes and nearby stars, proposing that as black holes gobble up nearby material, they “burp,” and the resulting winds affect the formation of nearby stars. Now, 20 years later, the experimental evidence has finally come in: Her theory seems correct. This hour, Ira talks with Priya about her theory. And Nergis Mavalvala of MIT joins to talk about why “squeezing light” may be the key to detecting more distant black hole collisions with the gravitational wave detector LIGO. Learn more here. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

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